1. Field of the Invention
The present invention relates to semiconductor device manufacturing, and more particularly, to methods of manufacturing non-volatile memory devices.
2. Description of the Related Art
Non-volatile memory devices are semiconductor memory devices that can retain stored data even if the power supply is abruptly interrupted. In recent years, owing to the increased demand for compact portable electronic products, such as portable multimedia reproduction devices, digital cameras, and personal digital assistants (PDAs), research into high-capacity high-integrated non-volatile memory devices for use in compact portable electronic products has rapidly progressed. Non-volatile memory devices may be classified into programmable read-only memories (PROMs), erasable and programmable read-only memories (EPROMs), and electrically erasable and programmable read-only memories (EEPROMs). A typical example of the non-volatile memory device is a flash memory device.
The flash memory device performs an erase operation and a rewrite operation in block units. Also, since the flash memory device has high integration and good data retention characteristics, the flash memory device may function as a main memory in a system and be used in an ordinary dynamic random access memory (DRAM) interface. Furthermore, since the flash memory device may be inexpensively fabricated, the flash memory device may be used as a subsidiary storage device instead of a conventional hard disk.
A cell transistor of a conventional flash memory includes a tunneling insulating layer disposed on a semiconductor substrate, a charge storage layer, a blocking insulating layer, and a control gate that are stacked sequentially. The flash memory device performs a write operation using a hot electron injection or Fowler-Nordheim tunneling (F-N tunneling) mechanism, and it performs an erase operation through the F-N tunneling mechanism. Cell characteristics of the flash memory device depend on the thickness of the tunneling insulating layer, a contact area between the charge storage layer and the semiconductor substrate, a contact area between the charge storage layer and the control gate, and/or the thickness of the blocking insulating layer. The cell characteristics of the flash memory device may include program speed, erase speed, the distribution of program cells, and the distribution of erase cells. Also, other characteristics related to the reliability of cells of the flash memory device are program/erase endurance and data retention.
As memory devices become smaller, it becomes more difficult to prevent current from leaking in insulating layers formed of silicon oxide, and thus research into high dielectric materials (i.e., high-k materials) that can be used as insulating layers in non-volatile memory devices, has been conducted. However, when high dielectric materials are used, undesirable charge capture due to defects included in the dielectric material can occur, thereby deteriorating the reliability of devices.